Hybrid wafer dicing approach using a rotating beam laser scribing process and plasma etch process

ABSTRACT

Methods of dicing semiconductor wafers, each wafer having a plurality of integrated circuits, are described. In an example, a method of dicing a semiconductor wafer having a plurality of integrated circuits involves forming a mask above the semiconductor wafer, the mask composed of a layer covering and protecting the integrated circuits. The mask is then patterned with a rotating laser beam laser scribing process to provide a patterned mask with gaps, exposing regions of the semiconductor wafer between the integrated circuits. The semiconductor wafer is then plasma etched through the gaps in the patterned mask to singulate the integrated circuits.

BACKGROUND

1) Field

Embodiments of the present invention pertain to the field ofsemiconductor processing and, in particular, to methods of dicingsemiconductor wafers, each wafer having a plurality of integratedcircuits thereon.

2) Description of Related Art

In semiconductor wafer processing, integrated circuits are formed on awafer (also referred to as a substrate) composed of silicon or othersemiconductor material. In general, layers of various materials whichare either semiconducting, conducting or insulating are utilized to formthe integrated circuits. These materials are doped, deposited and etchedusing various well-known processes to form integrated circuits. Eachwafer is processed to form a large number of individual regionscontaining integrated circuits known as dice.

Following the integrated circuit formation process, the wafer is “diced”to separate the individual die from one another for packaging or for usein an unpackaged form within larger circuits. The two main techniquesthat are used for wafer dicing are scribing and sawing. With scribing, adiamond tipped scribe is moved across the wafer surface along pre-formedscribe lines. These scribe lines extend along the spaces between thedice. These spaces are commonly referred to as “streets.” The diamondscribe forms shallow scratches in the wafer surface along the streets.Upon the application of pressure, such as with a roller, the waferseparates along the scribe lines. The breaks in the wafer follow thecrystal lattice structure of the wafer substrate. Scribing can be usedfor wafers that are about 10 mils (thousandths of an inch) or less inthickness. For thicker wafers, sawing is presently the preferred methodfor dicing.

With sawing, a diamond tipped saw rotating at high revolutions perminute contacts the wafer surface and saws the wafer along the streets.The wafer is mounted on a supporting member such as an adhesive filmstretched across a film frame and the saw is repeatedly applied to boththe vertical and horizontal streets. One problem with either scribing orsawing is that chips and gouges can form along the severed edges of thedice. In addition, cracks can form and propagate from the edges of thedice into the substrate and render the integrated circuit inoperative.Chipping and cracking are particularly a problem with scribing becauseonly one side of a square or rectangular die can be scribed in the<110>direction of the crystalline structure. Consequently, cleaving ofthe other side of the die results in a jagged separation line. Becauseof chipping and cracking, additional spacing is required between thedice on the wafer to prevent damage to the integrated circuits, e.g.,the chips and cracks are maintained at a distance from the actualintegrated circuits. As a result of the spacing requirements, not asmany dice can be formed on a standard sized wafer and wafer real estatethat could otherwise be used for circuitry is wasted. The use of a sawexacerbates the waste of real estate on a semiconductor wafer. The bladeof the saw is approximate 15 microns thick. As such, to insure thatcracking and other damage surrounding the cut made by the saw does notharm the integrated circuits, three to five hundred microns often mustseparate the circuitry of each of the dice. Furthermore, after cutting,each die requires substantial cleaning to remove particles and othercontaminants that result from the sawing process.

Plasma dicing has also been used, but may have limitations as well. Forexample, one limitation hampering implementation of plasma dicing may becost. A standard lithography operation for patterning resist may renderimplementation cost prohibitive. Another limitation possibly hamperingimplementation of plasma dicing is that plasma processing of commonlyencountered metals (e.g., copper) in dicing along streets can createproduction issues or throughput limits.

SUMMARY

Embodiments of the present invention include methods of, and apparatusesfor, dicing semiconductor wafers.

In an embodiment, a method of dicing a semiconductor wafer having aplurality of integrated circuits involves forming a mask above thesemiconductor wafer, the mask composed of a layer covering andprotecting the integrated circuits. The mask is then patterned with arotating beam laser scribing process to provide a patterned mask withgaps, exposing regions of the semiconductor wafer between the integratedcircuits. The semiconductor wafer is then plasma etched through the gapsin the patterned mask to singulate the integrated circuits.

In another embodiment, a method of dicing a semiconductor waferincluding a plurality of integrated circuits involves laser scribing thesemiconductor wafer with a rotating beam laser scribing process tosingulate the integrated circuits.

In another embodiment, a system for dicing a semiconductor wafer havinga plurality of integrated circuits includes a factory interface. Thesystem also includes a laser scribe apparatus coupled with the factoryinterface and having a laser assembly configured to provide a rotatinglaser beam. The system also includes a plasma etch chamber coupled withthe factory interface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a Flowchart representing operations in a method of dicing asemiconductor wafer including a plurality of integrated circuits, inaccordance with an embodiment of the present invention.

FIG. 2A illustrates a cross-sectional view of a semiconductor waferincluding a plurality of integrated circuits during performing of amethod of dicing the semiconductor wafer, corresponding to operation 102of the Flowchart of FIG. 1, in accordance with an embodiment of thepresent invention.

FIG. 2B illustrates a cross-sectional view of a semiconductor waferincluding a plurality of integrated circuits during performing of amethod of dicing the semiconductor wafer, corresponding to operation 104of the Flowchart of FIG. 1, in accordance with an embodiment of thepresent invention.

FIG. 2C illustrates a cross-sectional view of a semiconductor waferincluding a plurality of integrated circuits during performing of amethod of dicing the semiconductor wafer, corresponding to operation 108of the Flowchart of FIG. 1, in accordance with an embodiment of thepresent invention.

FIG. 3 is a flowchart representing operations of a laser scribingprocess with a rotating beam, in accordance with an embodiment of thepresent invention.

FIG. 4A illustrates the effect of rotating a Gaussian beam on-axis ofthe Gaussian beam, in accordance with an embodiment of the presentinvention.

FIG. 4B illustrates the effect of rotating a line-shaped beam having aflat top on-axis of the beam, in accordance with an embodiment of thepresent invention.

FIG. 4C illustrates the effect of rotating a line-shaped beam having aflat top off-axis of the beam, in accordance with an embodiment of thepresent invention.

FIG. 5A illustrates a schematic of a motor having a rotor with a corewhere rotating laser beam is output from a tubular light pipe housed inthe core of the rotor, in accordance with an embodiment of the presentinvention.

FIG. 5B illustrates a schematic of a motor having a rotor with a corewhere rotating laser beam is output from a cylindrical light pipe housedin the core of the rotor, in accordance with an embodiment of thepresent invention.

FIG. 6 illustrates the effects of using a laser pulse width in thefemtosecond range, picoseconds range, and nanosecond range, inaccordance with an embodiment of the present invention.

FIG. 7 illustrates a cross-sectional view of a stack of materials thatmay be used in a street region of a semiconductor wafer or substrate, inaccordance with an embodiment of the present invention.

FIGS. 8A-8D illustrate cross-sectional views of various operations in amethod of dicing a semiconductor wafer, in accordance with an embodimentof the present invention.

FIG. 9 illustrates a block diagram of a tool layout for laser and plasmadicing of wafers or substrates, in accordance with an embodiment of thepresent invention.

FIG. 10 illustrates a block diagram of an exemplary computer system, inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Methods of dicing semiconductor wafers, each wafer having a plurality ofintegrated circuits thereon, are described. In the followingdescription, numerous specific details are set forth, such as rotatingbeam laser scribing approaches and plasma etching conditions andmaterial regimes, in order to provide a thorough understanding ofembodiments of the present invention. It will be apparent to one skilledin the art that embodiments of the present invention may be practicedwithout these specific details. In other instances, well-known aspects,such as integrated circuit fabrication, are not described in detail inorder to not unnecessarily obscure embodiments of the present invention.Furthermore, it is to be understood that the various embodiments shownin the Figures are illustrative representations and are not necessarilydrawn to scale.

A hybrid wafer or substrate dicing process involving an initial laserscribe and subsequent plasma etch may be implemented for diesingulation. The laser scribe process may be used to cleanly remove amask layer, organic and inorganic dielectric layers, and device layers.The laser etch process may then be terminated upon exposure of, orpartial etch of, the wafer or substrate. The plasma etch portion of thedicing process may then be employed to etch through the bulk of thewafer or substrate, such as through bulk single crystalline silicon, toyield die or chip singulation or dicing. More specifically, one or moreembodiments are directed to implementing a rotating beam laser scribingprocess for, e.g., dicing applications.

Spatially uniform laser pulses by laser beam rotation for improved laserscribing process in hybrid laser dicing are described. Embodimentsinclude rotation of a beam as provided from a source, or rotation of analready shape laser beam. Advantages for rotating beam scribing mayinvolve, in a first embodiment, improving a process based on a lousybeam profile by providing an improved clean flat top beam profile and toachieve a scribed clean trench on the wafer. In another embodiment, adicing process based on an input lousy Gaussian laser beam profile isadvantageously improved by converting the beam into a clean Gaussianbeam profile using concentric rotation.

To provide context, in a hybrid wafer or substrate dicing processinvolving an initial laser scribe and subsequent plasma etch of a coatedwafer, a femtosecond laser may be applied to remove the mask and devicelayers on the dicing street until the silicon substrate is exposed. Aplasma etch follows to separate dies to realize die singulation.Typically, a non-rotated beam is used for the scribing process. However,a non-rotated beam may shows its limitation with the following twodifferent situations: (1) when a smooth sidewall is needed for a typicalnarrow kerf width or (2) when a wide kerf is demanded.

In accordance with one or more embodiments of the present invention, ascribing laser beam is rotated for improving laser scribing process inhybrid laser dicing. In additional embodiments, rotating of spatiallyshaped beams is implemented for improving laser scribing process inhybrid laser dicing processing schemes. In an embodiment, rotation ofthe beam is performed at a rotation rate approximately in the range of120 to 1200 rotations per minute (RPM). In one such embodiment, a lowerlimit is set as approximately 120 RPM to achieve a desired effect, e.g.,beam smoothing. In one embodiment, an upper limit is set based onreliability of rotation optics, e.g., in terms of vibration.

As such, in an aspect of the present invention, a combination of arotating beam laser scribing process with a plasma etching process maybe used to dice a semiconductor wafer into singulated integratedcircuits. FIG. 1 is a Flowchart 100 representing operations in a methodof dicing a semiconductor wafer including a plurality of integratedcircuits, in accordance with an embodiment of the present invention.FIGS. 2A-2C illustrate cross-sectional views of a semiconductor waferincluding a plurality of integrated circuits during performing of amethod of dicing the semiconductor wafer, corresponding to operations ofFlowchart 100, in accordance with an embodiment of the presentinvention.

Referring to operation 102 of Flowchart 100, and corresponding FIG. 2A,a mask 202 is formed above a semiconductor wafer or substrate 204. Themask 202 is composed of a layer covering and protecting integratedcircuits 206 formed on the surface of semiconductor wafer 204. The mask202 also covers intervening streets 207 formed between each of theintegrated circuits 206.

In accordance with an embodiment of the present invention, forming themask 202 includes forming a layer such as, but not limited to, aphoto-resist layer or an I-line patterning layer. For example, a polymerlayer such as a photo-resist layer may be composed of a materialotherwise suitable for use in a lithographic process. In one embodiment,the photo-resist layer is composed of a positive photo-resist materialsuch as, but not limited to, a 248 nanometer (nm) resist, a 193 nmresist, a 157 nm resist, an extreme ultra-violet (EUV) resist, or aphenolic resin matrix with a diazonaphthoquinone sensitizer. In anotherembodiment, the photo-resist layer is composed of a negativephoto-resist material such as, but not limited to, poly-cis-isoprene andpoly-vinyl-cinnamate.

In another embodiment, forming the mask 202 involves forming a layerdeposited in a plasma deposition process. For example, in one suchembodiment, the mask 202 is composed of a plasma deposited Teflon orTeflon-like (polymeric CF₂) layer. In a specific embodiment, thepolymeric CF₂ layer is deposited in a plasma deposition processinvolving the gas C₄F₈.

In another embodiment, forming the mask 202 involves forming awater-soluble mask layer. In an embodiment, the water-soluble mask layeris readily dissolvable in an aqueous media. For example, in oneembodiment, the water-soluble mask layer is composed of a material thatis soluble in one or more of an alkaline solution, an acidic solution,or in deionized water. In an embodiment, the water-soluble mask layermaintains its water solubility upon exposure to a heating process, suchas heating approximately in the range of 50-160 degrees Celsius. Forexample, in one embodiment, the water-soluble mask layer is soluble inaqueous solutions following exposure to chamber conditions used in alaser and plasma etch singulation process. In one embodiment, thewater-soluble mask layer is composed of a material such as, but notlimited to, polyvinyl alcohol, polyacrylic acid, dextran,polymethacrylic acid, polyethylene imine, or polyethylene oxide. In aspecific embodiment, the water-soluble mask layer has an etch rate in anaqueous solution approximately in the range of 1-15 microns per minuteand, more particularly, approximately 1.3 microns per minute.

In another embodiment, forming the mask 202 involves forming aUV-curable mask layer. In an embodiment, the mask layer has asusceptibility to UV light that reduces an adhesiveness of theUV-curable layer by at least approximately 80%. In one such embodiment,the UV layer is composed of polyvinyl chloride or an acrylic-basedmaterial. In an embodiment, the UV-curable layer is composed of amaterial or stack of materials with an adhesive property that weakensupon exposure to UV light. In an embodiment, the UV-curable adhesivefilm is sensitive to approximately 365 nm UV light. In one suchembodiment, this sensitivity enables use of LED light to perform a cure.

In an embodiment, semiconductor wafer or substrate 204 is composed of amaterial suitable to withstand a fabrication process and upon whichsemiconductor processing layers may suitably be disposed. For example,in one embodiment, semiconductor wafer or substrate 204 is composed of agroup IV-based material such as, but not limited to, crystallinesilicon, germanium or silicon/germanium. In a specific embodiment,providing semiconductor wafer 204 includes providing a monocrystallinesilicon substrate. In a particular embodiment, the monocrystallinesilicon substrate is doped with impurity atoms. In another embodiment,semiconductor wafer or substrate 204 is composed of a III-V materialsuch as, e.g., a III-V material substrate used in the fabrication oflight emitting diodes (LEDs).

In an embodiment, semiconductor wafer or substrate 204 has disposedthereon or therein, as a portion of the integrated circuits 206, anarray of semiconductor devices. Examples of such semiconductor devicesinclude, but are not limited to, memory devices or complimentarymetal-oxide-semiconductor (CMOS) transistors fabricated in a siliconsubstrate and encased in a dielectric layer. A plurality of metalinterconnects may be formed above the devices or transistors, and insurrounding dielectric layers, and may be used to electrically couplethe devices or transistors to form the integrated circuits 206.Materials making up the streets 207 may be similar to or the same asthose materials used to form the integrated circuits 206. For example,streets 207 may be composed of layers of dielectric materials,semiconductor materials, and metallization. In one embodiment, one ormore of the streets 207 includes test devices similar to the actualdevices of the integrated circuits 206.

Referring to operation 104 of Flowchart 100, and corresponding FIG. 2B,the mask 202 is patterned with a rotating laser beam laser scribingprocess to provide a patterned mask 208 with gaps 210, exposing regionsof the semiconductor wafer or substrate 204 between the integratedcircuits 206. In one such embodiment, the mask 202 is patterned with arotating shaped laser beam laser scribing process to provide thepatterned mask 208 with gaps 210. As such, the laser scribing process isused to remove the material of the streets 207 originally formed betweenthe integrated circuits 206. In accordance with an embodiment of thepresent invention, patterning the mask 202 with the rotating laser beamlaser scribing process includes forming trenches 212 partially into theregions of the semiconductor wafer 204 between the integrated circuits206, as depicted in FIG. 2B.

FIG. 3 is a flowchart 300 representing operations of a laser scribingprocess with a rotating beam, in accordance with an embodiment of thepresent invention. Referring to FIG. 3, at operation 302, a laser beamis input to or generated from a femto-second (Fs) laser oscillator. Atoperation 304, in an optional embodiment, the beam is then passed beamshaping optics. At operation 306, the beam obtained directly fromoperation 302, or the beam obtained from operation 304, is rotated. Atoperation 308, the output rotating beam from operation 306 is used in awafer scribing process. Thus, a laser scribing process with rotation ofa laser beam may be implemented. In an embodiment, for scribing trenchsize control, the beam shaping operation 304 is implemented in therotating beam process scheme.

In a first example of beam rotation, FIG. 4A illustrates the effect ofrotating a Gaussian beam on-axis of the Gaussian beam, in accordancewith an embodiment of the present invention. Referring to FIG. 4A, aninput Gaussian beam 400 having a central axis 402 has a relatively roughprofile. The input Gaussian beam 400 is rotated around axis 402 indirection 404 to provide a relatively smoother Gaussian output beam 406.Thus, in an embodiment, an input lousy Gaussian laser beam profile isconverted into a clean Gaussian beam profile by concentric rotation.

In a second example of beam rotation, FIG. 4B illustrates the effect ofrotating a line-shaped beam having a flat top on-axis of the beam, inaccordance with an embodiment of the present invention. Referring toFIG. 4B, an input line-shaped beam 410 having a flat top and having acentral axis 412 has a relatively rough profile. The input line-shapedbeam 410 having the flat top is rotated around axis 412 in direction 414to provide a relatively smoother input line-shaped beam 416 having aflat top. Thus, in an embodiment, a lousy beam profile provided aftershaping is subsequently improved to the clean flat top beam profile andis used in a laser scribing process to provide a scribed clean trench onthe wafer. In one embodiment, the input line-shaped beam 410 having theflat top is first obtained by inputting a Gaussian beam profile intoshaping optics to provide a line shaped flat top profile output from thebeam shaping optics. In a specific embodiment, the beam shaping opticsincludes a diffractive optical element, one or more slit aperture,axicons, etc.

In a third example of beam rotation, FIG. 4C illustrates the effect ofrotating a line-shaped beam having a flat top off-axis of the beam, inaccordance with an embodiment of the present invention. Referring toFIG. 4C, an input line-shaped beam 420 having a flat top and having anoff-set axis 422 has a relatively rough profile. The input line-shapedbeam 420 having the flat top is rotated around off-set axis 422 indirection 424 to provide a relatively smoother input line-shaped beam426 having a flat top. However, in one embodiment, since the rotationwas performed off-center, the resulting profile has a larger dimensionthan beam 416 of FIG. 4B. In one embodiment, using off-centered shiftedrotation controls the scribed trench size and provides for processvariety for selecting from various scribing schemes on a same wafer.

Thus, referring again to FIG. 4C, in an embodiment, a lousy beam profileprovided after shaping is subsequently improved to the clean flat topbeam profile and is used in a laser scribing process to provide ascribed clean trench on the wafer. In one embodiment, the inputline-shaped beam 420 having the flat top is first obtained by inputtinga Gaussian beam profile into shaping optics to provide a line shapedflat top profile output from the beam shaping optics. In a specificembodiment, the beam shaping optics includes a diffractive opticalelement, one or more slit aperture, axicons, etc.

In an aspect, a high laser pulse repetition process may be required forachieving high through-put of a laser application. To match the processrequirements, high speed control of rotated pulsed laser beam may thusbe needed. In an embodiment, using an electro-static/dynamic motor, alight pipe is inserted into the motor core to effect beam rotation,examples of which are described below in association with FIGS. 5A and5B.

In a first example, FIG. 5A illustrates a schematic of a motor having arotor with a core where rotating laser beam is output from a tubularlight pipe housed in the core of the rotor, in accordance with anembodiment of the present invention. A laser assembly includes a motor502 having a rotor 504 with a core 506. A rotating laser beam is outputfrom a tubular light pipe 508 housed in the core 506 of the rotor 504.In an embodiment, a tubular light pipe 508 is a light pipe having anannular shape with a hollow center, as is depicted in FIG. 5A.

In a second example, FIG. 5B illustrates a schematic of a motor having arotor with a core where rotating laser beam is output from a cylindricallight pipe housed in the core of the rotor, in accordance with anembodiment of the present invention. A laser assembly includes a motor512 having a rotor 514 with a core 516. A rotating laser beam is outputfrom a cylindrical light pipe 518 housed in the core 516 of the rotor514. In an embodiment, a cylindrical light pipe 518 is a light pipehaving a solid center, as is depicted in FIG. 5B.

In an embodiment, a femtosecond-based laser is used as a source for arotating laser beam or rotating shaped laser beam scribing process. Forexample, in an embodiment, a laser with a wavelength in the visiblespectrum plus the ultra-violet (UV) and infra-red (IR) ranges (totalinga broadband optical spectrum) is used to provide a femtosecond-basedlaser pulse, which has a pulse width on the order of the femtosecond(10⁻¹⁵ seconds). In one embodiment, ablation is not, or is essentiallynot, wavelength dependent and is thus suitable for complex films such asfilms of the mask 202, the streets 207 and, possibly, a portion of thesemiconductor wafer or substrate 204.

FIG. 6 illustrates the effects of using a laser pulse width in thefemtosecond range, picosecond range, and nanosecond range, in accordancewith an embodiment of the present invention. Referring to FIG. 6, byusing a laser beam in the femtosecond range, heat damage issues aremitigated or eliminated (e.g., minimal to no damage 602C withfemtosecond processing of a via 600C) versus longer pulse widths (e.g.,significant damage 602A with nanosecond processing of a via 600A). Theelimination or mitigation of damage during formation of via 600C may bedue to a lack of low energy recoupling (as is seen for picosecond-basedlaser ablation of 600B/602B) or thermal equilibrium (as is seen fornanosecond-based laser ablation), as depicted in FIG. 6.

Laser parameters selection, such as beam profile, may be critical todeveloping a successful laser scribing and dicing process that minimizeschipping, microcracks and delamination in order to achieve clean laserscribe cuts. The cleaner the laser scribe cut, the smoother an etchprocess that may be performed for ultimate die singulation. Insemiconductor device wafers, many functional layers of differentmaterial types (e.g., conductors, insulators, semiconductors) andthicknesses are typically disposed thereon. Such materials may include,but are not limited to, organic materials such as polymers, metals, orinorganic dielectrics such as silicon dioxide and silicon nitride.

A street between individual integrated circuits disposed on a wafer orsubstrate may include the similar or same layers as the integratedcircuits themselves. For example, FIG. 7 illustrates a cross-sectionalview of a stack of materials that may be used in a street region of asemiconductor wafer or substrate, in accordance with an embodiment ofthe present invention.

Referring to FIG. 7, a street region 700 includes the top portion 702 ofa silicon substrate, a first silicon dioxide layer 704, a first etchstop layer 706, a first low K dielectric layer 708 (e.g., having adielectric constant of less than the dielectric constant of 4.0 forsilicon dioxide), a second etch stop layer 710, a second low Kdielectric layer 712, a third etch stop layer 714, an undoped silicaglass (USG) layer 716, a second silicon dioxide layer 718, and a layerof photo-resist 720, with relative thicknesses depicted. Coppermetallization 722 is disposed between the first and third etch stoplayers 706 and 714 and through the second etch stop layer 710. In aspecific embodiment, the first, second and third etch stop layers 706,710 and 714 are composed of silicon nitride, while low K dielectriclayers 708 and 712 are composed of a carbon-doped silicon oxidematerial.

Under conventional laser irradiation (such as nanosecond-basedirradiation), the materials of street 700 behave quite differently interms of optical absorption and ablation mechanisms. For example,dielectrics layers such as silicon dioxide, is essentially transparentto all commercially available laser wavelengths under normal conditions.By contrast, metals, organics (e.g., low K materials) and silicon cancouple photons very easily, particularly in response to nanosecond-basedirradiation. In an embodiment, a line shaped profile laser beam laserscribing process is used to pattern a layer of silicon dioxide, a layerof low K material, and a layer of copper by ablating the layer ofsilicon dioxide prior to ablating the layer of low K material and thelayer of copper.

In case that the rotating laser beam or rotating shaped laser beam is afemtosecond-based laser beam, in an embodiment, suitablefemtosecond-based laser processes are characterized by a high peakintensity (irradiance) that usually leads to nonlinear interactions invarious materials. In one such embodiment, the femtosecond laser sourceshave a pulse width approximately in the range of 10 femtoseconds to 500femtoseconds, although preferably in the range of 100 femtoseconds to400 femtoseconds. In one embodiment, the femtosecond laser sources havea wavelength approximately in the range of 1570 nanometers to 200nanometers, although preferably in the range of 540 nanometers to 250nanometers. In one embodiment, the laser and corresponding opticalsystem provide a focal spot at the work surface approximately in therange of 3 microns to 15 microns, though preferably approximately in therange of 5 microns to 10 microns or between 10-15 microns.

In an embodiment, the laser source has a pulse repetition rateapproximately in the range of 200 kHz to 10 MHz, although preferablyapproximately in the range of 500 kHz to 5 MHz. In an embodiment, thelaser source delivers pulse energy at the work surface approximately inthe range of 0.5 uJ to 100 uJ, although preferably approximately in therange of 1 uJ to 5 uJ. In an embodiment, the laser scribing process runsalong a work piece surface at a speed approximately in the range of 500mm/sec to 5 m/sec, although preferably approximately in the range of 600mm/sec to 2 m/sec.

The scribing process may be run in single pass only, or in multiplepasses, but, in an embodiment, preferably 1-2 passes. In one embodiment,the scribing depth in the work piece is approximately in the range of 5microns to 50 microns deep, preferably approximately in the range of 10microns to 20 microns deep. In an embodiment, the kerf width of thelaser beam generated is approximately in the range of 2 microns to 15microns, although in silicon wafer scribing/dicing preferablyapproximately in the range of 6 microns to 10 microns, measured at thedevice/silicon interface.

Laser parameters may be selected with benefits and advantages such asproviding sufficiently high laser intensity to achieve ionization ofinorganic dielectrics (e.g., silicon dioxide) and to minimizedelamination and chipping caused by underlayer damage prior to directablation of inorganic dielectrics. Also, parameters may be selected toprovide meaningful process throughput for industrial applications withprecisely controlled ablation width (e.g., kerf width) and depth. In anembodiment, a line shaped profile laser beam laser scribing process issuitable to provide such advantages.

It is to be appreciated that the dicing or singulation process could bestopped after the above described laser scribing in a case that thelaser scribing is used to pattern the mask as well as to scribe fullythrough the wafer or substrate in order to singulate the dies.Accordingly, further singulation processing would not be required insuch a case. However, the following embodiments may be considered incases where laser scribing alone is not implemented for totalsingulation.

Referring now to optional operation 106 of Flowchart 100, anintermediate post mask-opening cleaning operation is performed. In anembodiment, the post mask-opening cleaning operation is a plasma-basedcleaning process. In a first example, as described below, theplasma-based cleaning process is reactive to the regions of thesubstrate 204 exposed by the gaps 210. In the case of a reactiveplasma-based cleaning process, the cleaning process itself may form orextend trenches 212 in the substrate 204 since the reactive plasma-basedcleaning operation is at least somewhat of an etchant for the substrate204. In a second, different, example, as is also described below, theplasma-based cleaning process is non-reactive to the regions of thesubstrate 204 exposed by the gaps 210.

In accordance with a first embodiment, the plasma-based cleaning processis reactive to exposed regions of the substrate 204 in that the exposedregions are partially etched during the cleaning process. In one suchembodiment, Ar or another non-reactive gas (or the mix) is combined withSF₆ for a highly-biased plasma treatment for cleaning of scribedopenings. The plasma treatment using mixed gases Ar+SF₆ under high-biaspower is performed for bombarding mask-opened regions to achievecleaning of the mask-opened regions. In the reactive breakthroughprocess, both physical bombardment from Ar and SF₆ along with chemicaletching due to SF₆ and F-ions contribute to cleaning of mask-openedregions. The approach may be suitable for photoresist orplasma-deposited Teflon masks 202, where breakthrough treatment leads tofairly uniform mask thickness reduction and a gentle Si etch. Such abreakthrough etch process, however, may not be best suited for watersoluble mask materials.

In accordance with a second embodiment, the plasma-based cleaningprocess is non-reactive to exposed regions of the substrate 204 in thatthe exposed regions are not or only negligible etched during thecleaning process. In one such embodiment, only non-reactive gas plasmacleaning is used. For example, Ar or another non-reactive gas (or themix) is used to perform a highly-biased plasma treatment both for maskcondensation and cleaning of scribed openings. The approach may besuitable for water-soluble masks or for thinner plasma-deposited Teflon202. In another such embodiment, separate mask condensation and scribedtrench cleaning operations are used, e.g., an Ar or non-reactive gas (orthe mix) highly-biased plasma treatment for mask condensation is firstperformed, and then an Ar+SF₆ plasma cleaning of a laser scribed trenchis performed. This embodiment may be suitable for cases whereAr-cleaning is not sufficient for trench cleaning due to too thick of amask material. Cleaning efficiency is improved for thinner masks, butmask etch rate is much lower, with almost no consumption in a subsequentdeep silicon etch process. In yet another such embodiment,three-operation cleaning is performed: (a) Ar or non-reactive gas (orthe mix) highly-biased plasma treatment for mask condensation, (b)Ar+SF₆ highly-biased plasma cleaning of laser scribed trenches, and (c)Ar or non-reactive gas (or the mix) highly-biased plasma treatment formask condensation. In accordance with another embodiment of the presentinvention, a plasma cleaning operation involves first use of a reactiveplasma cleaning treatment, such as described above in the first aspectof operation 106. The reactive plasma cleaning treatment is thenfollowed by a non-reactive plasma cleaning treatment such as describedin association with the second aspect of operation 106.

Referring to operation 108 of Flowchart 100, and corresponding FIG. 2C,the semiconductor wafer 204 is etched through the gaps 210 in thepatterned mask 208 to singulate the integrated circuits 206. Inaccordance with an embodiment of the present invention, etching thesemiconductor wafer 204 includes ultimately etching entirely throughsemiconductor wafer 204, as depicted in FIG. 2C, by etching the trenches212 initially formed with the rotating laser beam or rotating shapedlaser beam laser scribing process.

In an embodiment, patterning the mask with the laser scribing processinvolves forming trenches in the regions of the semiconductor waferbetween the integrated circuits, and plasma etching the semiconductorwafer involves extending the trenches to form corresponding trenchextensions. In one such embodiment, each of the trenches has a width,and each of the corresponding trench extensions has the width.

In accordance with an embodiment of the present invention, the resultingroughness of mask opening from laser scribing can impact die sidewallquality resulting from the subsequent formation of a plasma etchedtrench. Lithographically opened masks often have smooth profiles,leading to smooth corresponding sidewalls of a plasma etched trench. Bycontrast, a conventional laser opened mask can have a very rough profilealong a scribing direction if improper laser process parameters areselected (such as spot overlap, leading to rough sidewall of plasmaetched trench horizontally). Although the surface roughness can besmoothened by additional plasma processes, there is a cost andthroughput hit to remedying such issues. Accordingly, embodimentsdescribed herein may be advantageous in providing a smoother scribingprocess from the laser scribing portion of the singulation process.

In an embodiment, etching the semiconductor wafer 204 includes using aplasma etching process. In one embodiment, a through-silicon via typeetch process is used. For example, in a specific embodiment, the etchrate of the material of semiconductor wafer 204 is greater than 25microns per minute. An ultra-high-density plasma source may be used forthe plasma etching portion of the die singulation process. An example ofa process chamber suitable to perform such a plasma etch process is theApplied Centura® Silvia™ Etch system available from Applied Materials ofSunnyvale, Calif., USA. The Applied Centura® Silvia™ Etch systemcombines the capacitive and inductive RF coupling, which gives much moreindependent control of the ion density and ion energy than was possiblewith the capacitive coupling only, even with the improvements providedby magnetic enhancement. This combination enables effective decouplingof the ion density from ion energy, so as to achieve relatively highdensity plasmas without the high, potentially damaging, DC bias levels,even at very low pressures. This results in an exceptionally wideprocess window. However, any plasma etch chamber capable of etchingsilicon may be used. In an exemplary embodiment, a deep silicon etch isused to etch a single crystalline silicon substrate or wafer 204 at anetch rate greater than approximately 40% of conventional silicon etchrates while maintaining essentially precise profile control andvirtually scallop-free sidewalls. In a specific embodiment, athrough-silicon via type etch process is used. The etch process is basedon a plasma generated from a reactive gas, which generally afluorine-based gas such as SF₆, C₄F₈, CHF₃, XeF₂, or any other reactantgas capable of etching silicon at a relatively fast etch rate. In anembodiment, the mask layer 208 is removed after the singulation process,as depicted in FIG. 2C. In another embodiment, the plasma etchingoperation described in association with FIG. 2C employs a conventionalBosch-type dep/etch/dep process to etch through the substrate 204.Generally, a Bosch-type process consists of three sub-operations:deposition, a directional bombardment etch, and isotropic chemical etchwhich is run through many iterations (cycles) until silicon is etchedthrough.

Accordingly, referring again to Flowchart 100 and FIGS. 2A-2C, waferdicing may be preformed by initial ablation using a rotating laser beamor rotating shaped laser beam laser scribing process to ablate through amask layer, through wafer streets (including metallization), andpartially into a silicon substrate. Die singulation may then becompleted by subsequent through-silicon deep plasma etching. A specificexample of a materials stack for dicing is described below inassociation with FIGS. 8A-8D, in accordance with an embodiment of thepresent invention.

Referring to FIG. 8A, a materials stack for hybrid laser ablation andplasma etch dicing includes a mask layer 802, a device layer 804, and asubstrate 806. The mask layer, device layer, and substrate are disposedabove a die attach film 808 which is affixed to a backing tape 810. Inan embodiment, the mask layer 802 is a water soluble layer such as thewater soluble layers described above in association with mask 202. Thedevice layer 804 includes an inorganic dielectric layer (such as silicondioxide) disposed above one or more metal layers (such as copper layers)and one or more low K dielectric layers (such as carbon-doped oxidelayers). The device layer 804 also includes streets arranged betweenintegrated circuits, the streets including the same or similar layers tothe integrated circuits. The substrate 806 is a bulk single-crystallinesilicon substrate.

In an embodiment, the bulk single-crystalline silicon substrate 806 isthinned from the backside prior to being affixed to the die attach film808. The thinning may be performed by a backside grind process. In oneembodiment, the bulk single-crystalline silicon substrate 806 is thinnedto a thickness approximately in the range of 50-100 microns. It isimportant to note that, in an embodiment, the thinning is performedprior to a laser ablation and plasma etch dicing process. In anembodiment, the photo-resist layer 802 has a thickness of approximately5 microns and the device layer 804 has a thickness approximately in therange of 2-3 microns. In an embodiment, the die attach film 808 (or anysuitable substitute capable of bonding a thinned or thin wafer orsubstrate to the backing tape 810) has a thickness of approximately 20microns.

Referring to FIG. 8B, the mask 802, the device layer 804 and a portionof the substrate 806 are patterned with a rotating laser beam orrotating shaped laser beam laser scribing process 812 to form trenches814 in the substrate 806. Referring to FIG. 8C, a through-silicon deepplasma etch process 816 is used to extend the trench 814 down to the dieattach film 808, exposing the top portion of the die attach film 808 andsingulating the silicon substrate 806. The device layer 804 is protectedby the mask layer 802 during the through-silicon deep plasma etchprocess 816.

Referring to FIG. 8D, the singulation process may further includepatterning the die attach film 808, exposing the top portion of thebacking tape 810 and singulating the die attach film 808. In anembodiment, the die attach film is singulated by a laser process or byan etch process. Further embodiments may include subsequently removingthe singulated portions of substrate 806 (e.g., as individual integratedcircuits) from the backing tape 810. In one embodiment, the singulateddie attach film 808 is retained on the back sides of the singulatedportions of substrate 806. Other embodiments may include removing themask layer 802 from the device layer 804. In an alternative embodiment,in the case that substrate 806 is thinner than approximately 50 microns,the rotating laser beam or rotating shaped laser beam laser scribingprocess 812 is used to completely singulate substrate 806 without theuse of an additional plasma process.

A single process tool may be configured to perform many or all of theoperations in a hybrid line shaped profile laser beam ablation andplasma etch singulation process. For example, FIG. 9 illustrates a blockdiagram of a tool layout for laser and plasma dicing of wafers orsubstrates, in accordance with an embodiment of the present invention.

Referring to FIG. 9, a process tool 900 includes a factory interface 902(FI) having a plurality of load locks 904 coupled therewith. A clustertool 906 is coupled with the factory interface 902. The cluster tool 906includes one or more plasma etch chambers, such as plasma etch chamber908. A laser scribe apparatus 910 is also coupled to the factoryinterface 902. The overall footprint of the process tool 900 may be, inone embodiment, approximately 3500 millimeters (3.5 meters) byapproximately 3800 millimeters (3.8 meters), as depicted in FIG. 9.

In an embodiment, the laser scribe apparatus 910 houses a laser assemblyconfigured to provide a rotating laser beam. In one such embodiment, thelaser assembly is configured to provide a rotating shaped laser beam. Ina specific such embodiment, the laser assembly is configured to providethe rotating laser beam as a rotating shaped laser beam, the laserassembly including beam shaping optics selected from the groupconsisting of a diffractive optical element, one or more slit aperture,and axicons.

In an embodiment, the laser assembly is configured to rotate a laserbeam around an on-axis of an input laser beam. In another embodiment,the laser assembly is configured to rotate a laser beam around anoff-axis of an input laser beam. In either case, in a particularembodiment, the laser beam is a femto-second based laser beam.

In an embodiment, the laser assembly comprises a motor having a rotorwith a core. The rotating laser beam is output from a tubular light pipehoused in the core of the rotor, an example of which is described abovein association with FIG. 5A. In another embodiment, the laser assemblycomprises a motor having a rotor with a core. The rotating laser beam isoutput from a cylindrical light pipe housed in the core of the rotor, anexample of which is described above in association with FIG. 5B.

In an embodiment, the laser is suitable for performing a laser ablationportion of a hybrid laser and etch singulation process, such as thelaser ablation processes described above. In one embodiment, a moveablestage is also included in laser scribe apparatus 910, the moveable stageconfigured for moving a wafer or substrate (or a carrier thereof)relative to the laser. In a specific embodiment, the laser is alsomoveable. The overall footprint of the laser scribe apparatus 910 maybe, in one embodiment, approximately 2240 millimeters by approximately1270 millimeters, as depicted in FIG. 9.

In an embodiment, the one or more plasma etch chambers 908 is configuredfor etching a wafer or substrate through the gaps in a patterned mask tosingulate a plurality of integrated circuits. In one such embodiment,the one or more plasma etch chambers 908 is configured to perform a deepsilicon etch process. In a specific embodiment, the one or more plasmaetch chambers 808 is an Applied Centura® Silvia™ Etch system, availablefrom Applied Materials of Sunnyvale, Calif., USA. The etch chamber maybe specifically designed for a deep silicon etch used to createsingulate integrated circuits housed on or in single crystalline siliconsubstrates or wafers. In an embodiment, a high-density plasma source isincluded in the plasma etch chamber 908 to facilitate high silicon etchrates. In an embodiment, more than one etch chamber is included in thecluster tool 906 portion of process tool 900 to enable highmanufacturing throughput of the singulation or dicing process.

The factory interface 902 may be a suitable atmospheric port tointerface between an outside manufacturing facility with laser scribeapparatus 910 and cluster tool 906. The factory interface 902 mayinclude robots with arms or blades for transferring wafers (or carriersthereof) from storage units (such as front opening unified pods) intoeither cluster tool 906 or laser scribe apparatus 910, or both.

Cluster tool 906 may include other chambers suitable for performingfunctions in a method of singulation. For example, in one embodiment, inplace of an additional etch chamber, a deposition chamber 912 isincluded. The deposition chamber 912 may be configured for maskdeposition on or above a device layer of a wafer or substrate prior tolaser scribing of the wafer or substrate. In one such embodiment, thedeposition chamber 912 is suitable for depositing a photo-resist layer.In another embodiment, in place of an additional etch chamber, a wet/drystation 914 is included. The wet/dry station may be suitable forcleaning residues and fragments, or for removing a mask, subsequent to alaser scribe and plasma etch singulation process of a substrate orwafer. In yet another embodiment, in place of an additional deep siliconetch chamber, a plasma etch chamber is included and is configured forperforming a plasma-based cleaning process. In an embodiment, ametrology station is also included as a component of process tool 900.

Embodiments of the present invention may be provided as a computerprogram product, or software, that may include a machine-readable mediumhaving stored thereon instructions, which may be used to program acomputer system (or other electronic devices) to perform a processaccording to embodiments of the present invention. In one embodiment,the computer system is coupled with process tool 900 described inassociation with FIG. 9. A machine-readable medium includes anymechanism for storing or transmitting information in a form readable bya machine (e.g., a computer). For example, a machine-readable (e.g.,computer-readable) medium includes a machine (e.g., a computer) readablestorage medium (e.g., read only memory (“ROM”), random access memory(“RAM”), magnetic disk storage media, optical storage media, flashmemory devices, etc.), a machine (e.g., computer) readable transmissionmedium (electrical, optical, acoustical or other form of propagatedsignals (e.g., infrared signals, digital signals, etc.)), etc.

FIG. 10 illustrates a diagrammatic representation of a machine in theexemplary form of a computer system 1000 within which a set ofinstructions, for causing the machine to perform any one or more of themethodologies described herein, may be executed. In alternativeembodiments, the machine may be connected (e.g., networked) to othermachines in a Local Area Network (LAN), an intranet, an extranet, or theInternet. The machine may operate in the capacity of a server or aclient machine in a client-server network environment, or as a peermachine in a peer-to-peer (or distributed) network environment. Themachine may be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, a webappliance, a server, a network router, switch or bridge, or any machinecapable of executing a set of instructions (sequential or otherwise)that specify actions to be taken by that machine. Further, while only asingle machine is illustrated, the term “machine” shall also be taken toinclude any collection of machines (e.g., computers) that individuallyor jointly execute a set (or multiple sets) of instructions to performany one or more of the methodologies described herein.

The exemplary computer system 1000 includes a processor 1002, a mainmemory 1004 (e.g., read-only memory (ROM), flash memory, dynamic randomaccess memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM(RDRAM), etc.), a static memory 1006 (e.g., flash memory, static randomaccess memory (SRAM), MRAM, etc.), and a secondary memory 1018 (e.g., adata storage device), which communicate with each other via a bus 1030.

Processor 1002 represents one or more general-purpose processing devicessuch as a microprocessor, central processing unit, or the like. Moreparticularly, the processor 1002 may be a complex instruction setcomputing (CISC) microprocessor, reduced instruction set computing(RISC) microprocessor, very long instruction word (VLIW) microprocessor,processor implementing other instruction sets, or processorsimplementing a combination of instruction sets. Processor 1002 may alsobe one or more special-purpose processing devices such as an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), a digital signal processor (DSP), network processor, or thelike. Processor 1002 is configured to execute the processing logic 1026for performing the operations described herein.

The computer system 1000 may further include a network interface device1008. The computer system 1000 also may include a video display unit1010 (e.g., a liquid crystal display (LCD), a light emitting diodedisplay (LED), or a cathode ray tube (CRT)), an alphanumeric inputdevice 1012 (e.g., a keyboard), a cursor control device 1014 (e.g., amouse), and a signal generation device 1016 (e.g., a speaker).

The secondary memory 1018 may include a machine-accessible storagemedium (or more specifically a computer-readable storage medium) 1032 onwhich is stored one or more sets of instructions (e.g., software 1022)embodying any one or more of the methodologies or functions describedherein. The software 1022 may also reside, completely or at leastpartially, within the main memory 1004 and/or within the processor 1002during execution thereof by the computer system 1000, the main memory1004 and the processor 1002 also constituting machine-readable storagemedia. The software 1022 may further be transmitted or received over anetwork 1020 via the network interface device 1008.

While the machine-accessible storage medium 1032 is shown in anexemplary embodiment to be a single medium, the term “machine-readablestorage medium” should be taken to include a single medium or multiplemedia (e.g., a centralized or distributed database, and/or associatedcaches and servers) that store the one or more sets of instructions. Theterm “machine-readable storage medium” shall also be taken to includeany medium that is capable of storing or encoding a set of instructionsfor execution by the machine and that cause the machine to perform anyone or more of the methodologies of the present invention. The term“machine-readable storage medium” shall accordingly be taken to include,but not be limited to, solid-state memories, and optical and magneticmedia.

In accordance with an embodiment of the present invention, amachine-accessible storage medium has instructions stored thereon whichcause a data processing system to perform a method of dicing asemiconductor wafer having a plurality of integrated circuits. Themethod includes forming a mask above the semiconductor wafer, the maskcomposed of a layer covering and protecting the integrated circuits. Themask is then patterned with a rotating laser beam laser scribing processto provide a patterned mask with gaps, exposing regions of thesemiconductor wafer between the integrated circuits. The semiconductorwafer is then plasma etched through the gaps in the patterned mask tosingulate the integrated circuits.

Thus, hybrid wafer dicing approaches using a rotating laser beam orrotating shaped laser beam, and plasma etch process, have beendisclosed.

What is claimed is:
 1. A method of dicing a semiconductor wafercomprising a plurality of integrated circuits, the method comprising:forming a mask above the semiconductor wafer, the mask comprising alayer covering and protecting the integrated circuits; patterning themask with a rotating laser beam laser scribing process to provide apatterned mask with gaps, exposing regions of the semiconductor waferbetween the integrated circuits, wherein the rotating laser beam laserscribing process comprises rotating a laser beam around a central axisof the laser beam along a direction of travel of the laser beam; andplasma etching the semiconductor wafer through the gaps in the patternedmask to singulate the integrated circuits.
 2. The method of claim 1,wherein the rotating laser beam laser scribing process is a rotatingshaped laser beam laser scribing process.
 3. The method of claim 1,wherein the rotating laser beam laser scribing process is based on asmooth Gaussian beam.
 4. The method of claim 1, wherein the rotatinglaser beam laser scribing process is based on a smooth line-shaped beamhaving a flat top.
 5. The method of claim 1, wherein scribing with therotating laser beam laser scribing process comprises scribing with arotating femto-second based laser beam.
 6. The method of claim 1,wherein patterning the mask with the laser scribing process comprisesforming trenches in the regions of the semiconductor wafer between theintegrated circuits, and wherein plasma etching the semiconductor wafercomprises extending the trenches to form corresponding trenchextensions.
 7. A method of dicing a semiconductor wafer comprising aplurality of integrated circuits, the method comprising: providing asemiconductor wafer having a mask thereon, the mask comprising a layercovering and protecting the integrated circuits; patterning the maskwith a rotating laser beam laser scribing process to provide a patternedmask with gaps, exposing regions of the semiconductor wafer between theintegrated circuits, wherein the rotating laser beam laser scribingprocess comprises rotating a laser beam around a central axis of thelaser beam along a direction of travel of the laser beam; and plasmaetching the semiconductor wafer through the gaps in the patterned maskto singulate the integrated circuits.
 8. The method of claim 7, whereinthe rotating laser beam laser scribing process is a rotating shapedlaser beam laser scribing process.
 9. The method of claim 7, wherein therotating laser beam laser scribing process is based on a smooth Gaussianbeam.
 10. The method of claim 7, wherein the rotating laser beam laserscribing process is based on a smooth line-shaped beam having a flattop.
 11. The method of claim 7, wherein scribing with the rotating laserbeam laser scribing process comprises scribing with a rotatingfemto-second based laser beam.
 12. The method of claim 7, whereinpatterning the mask with the laser scribing process comprises formingtrenches in the regions of the semiconductor wafer between theintegrated circuits, and wherein plasma etching the semiconductor wafercomprises extending the trenches to form corresponding trenchextensions.